The present invention relates generally to video signal processing circuits for colour television cameras and more particularly to a video signal, envelope detection circuit for processing amplitude-modulated wave color signals obtained from the image pickup, camera tube of a color television camera. Then, the signal is immediately processed and amplified, and thereafter it is matrixed.
In a known video signal processing circuit for color television cameras, as will be hereinafter described more fully with reference to a drawing, amplitude-modulated wave colour signals are matrixed after being detected. The resulting signals are then subjected to signal processing amplification. For this reason, the DC components of the signals are restored during their detection, and their black levels are made constant. However, when the detected output signals pass through the matrixing circuit, which is an AC coupling, the black levels which should be constant lose their constant characteristics.
For this reason, at the time of process amplification of the output signals of the matrixing circuit, the known circuit must restore the DC component a second time. Accordingly, clamping circuits such as pulse clamping circuits or diode clamping circuits become necessary in the processing amplifiers, whereby problems occur, such as complication of the circuit and an impossibility of obtaining a composite colour video signal of high stability.
Moreover, in known processing methods, an amplitude-modulated signal is directly subjected processing, before detection occurs. This processing method, however, gives rise to a difficulty in that it requires a complicated circuit for causing an average picture level to assume zero.
Furthermore, a circuit may be devised in which the entire system extending from detection circuits through a matrix circuit to processing amplifiers is constituted by DC couplings. However, since the matrix circuit is interposed between the detection circuits to the processing amplifiers, the above described circuit system becomes too long, and the stability of the signal becomes poor.